Tunable resonant ring utilizing strip transmission line



Dec. 7, 1965 H. s. KEEN 3,222,624

TUNABLE RESONANT RING UTILIZING STRIP TRANSMISSION LINE Filed Nov. 7,1960 2 Sheets-Sheet l 2 1 6 2 &

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TUNABLE RESONANT RING UTILIZING STRIP TRANSMISSION LINE Filed Nov. '7,1960 2 Sheets-Sheet 2 IN V EN TOR.

Mam/xiv @5- A z/v BY WW Aim- 647700616 United States Patent TUNABLERESONANT RING UTILIZING STRIP TRANSMISSION LINE Henry S. Keen,Uniondale, N.Y., assignor to the United States of America as representedby the Secretary of the Air Force Filed Nov. 7, 1960, Ser. No. 67,866 4Claims. (Cl. 33382) This invention relates to a tunable microwaveresonant circuit and more particularly to a ring strip transmission linecircuit having a variable resonant frequency.

In the prior art, strip transmission line circuits have had widespreadutility in the microwave regions such as shown and described in theProceeding of I.R.E. No. 40, December 1952, page 164417; In theapplication of strip transmission line techniques, a resonant circuithas evolved such as shown and described in United States Patent No.2,922,123 issued January 19, 1960. However, a limitation of theaforesaid resonant strip transmission line circuit has been the lack ofa simple, effective means for varying the frequency of resonancethereof. The present invention provides a tunable microwave circuitcapable of being adjusted to transmit microwave energy at any desiredfrequency within its tuning range. A strip transmission line ring with amean circumference of one wavelength is capacitively or inductivelycoupled at diametrically opposite points. A metallic element is insertedconcentrically within aforesaid ring and is rotated about the axis ofthe ring thereby varying the resonant frequency of the ring by itseffect upon the electric field and the magnetic field thereof.

An object of the present invention is to provide a strip transmissionline ring circuit having a variable resonant frequency.

Another object of the present invention is to provide a striptransmission line ring with a rotatable metallic slug disposedconcentrically within said ring.

Yet another object of the present invention is to provide a tunablemicrowave resonant circuit wherein microwave energy is transmitted atany desired frequency within its tuning range.

In the accompanying drawings which form part of the instantspecification and which are to be read in conjunction therewith and inwhich like reference numerals are used to indicate like parts in thevarious views:

FIGURE 1 shows apparatus embodying my invention wherein the resonantring is shown at the low frequency position;

FIGURE 2 is identical to FIGURE 1 but illustrating the high resonantfrequency position thereof;

FIGURE 3 illustrates an elevation view, partly in section, of thetunable resonant ring of FIGURE 1;

FIGURE 4 shows a second embodiment of my invention; and

FIGURE 5 is an elevation view, partly in section, of the tunableresonant ring of FIGURE 4.

Now referring in detail to FIGURE 1, there is shown a top view of myinvention with the ground planes omitted for purposes of clarity.Conventional strip transmission line ring has energy coupled thereto byway of input strip transmission line 11 and microwave energy istransmitted therefrom by coupling output strip transmission line 12thereto. Strip transmission line ring 10 has a mean circumference of onewavelength and, as illustrated, input coupling line 11 and outputcoupling line 12 are at diametrically opposed points. It is to be notedthat the coupling of energy into and out of ring 11) may be accomplishedeither capacitively or inductively.

Metallic element 14 is inserted within the inner periphery of ring 10and is concentric therewith. Metallic element 14 is a solid piece ofmetal, such as copper,

which is in the shape of a butterfly and is rotatable on an axis throughthe center of ring 10. Point 13 represents ground at one node.

Now referring to FIGURE 3, there is shown parallel ground planes 2t) and21 affixed to insulating cylinder 22 and spaced thereby. Parallel groundplanes 2t) and 21 were omitted from FIGURES 1 and 2 for purposes ofclarity. Resonant ring 10 is positioned between ground planes 20 and 21and is also parallel thereto. Resonant ring 10 is affixed to andpositioned by means of supporting dielectric 23. Supporting dielectric23, in turn, is affixed to insulating cylinder 22. Supporting dielectric23 may be comprised of Tefion glass. Rotor 14 is positioned centrally inground planes 20 and 21 through apertures 24 and 25 by means of extendedshafts 26 and 27, respectively. Extended shafts 26 and 27 are made ofinsulating material and are integrated with rotor 14. Rotor 14 is turnedby means of shaft 27.

Now referring to FIGURE 1, in operation, energy is coupled into striptransmission line ring 10 by way of strip transmission line input 11.Rotor 14, in the low frequency position, capacitively loads resonantring 10, as it is located at the voltage points. In the high frequencyposition, as shown in FIGURE 2, the effect is to restrict the magneticfield, thereby raising the resonant frequency of ring 10. Energy iscoupled out of resonant ring 19 by way of output strip transmission line12. Thus, there is provided a tunable microwave resonant circuit capableof being adjusted to transmit microwave energy at any desired frequencywithin its range. The means for coupling in and out of resonant ring 10is conventional and is shown and described in United States Patent No.2,922,123 issued January 19, 1960.

Now referring to FIGURE 4, there is shown another embodiment of myinvention in which butterfly rotor element 14 is made with a largerdiameter than the inner diameter of resonant ring 10. A groove is cut inrotor element 14 to allow resonant ring 10 to pass. This is more clearlyillustrated in FIGURE 5 in which groove 28 has been cut in rotor 14. Theconstruction and operation of my second embodiment is identical to theoperation of my embodiment as illustrated in FIGURE 1; however, thegrooving arrangement of rotor 14 permits a greater variation in thefrequency of resonance in strip transmission line ring 10. For example,with rotor 14 made of copper, the resonant frequency varied from 2,538megacycles for 0 rotation to 3,390 megacycles for rotation. It is to benoted that each of the described embodiments of my invention may also beutilized as tunable filters.

Although in accordance with the provisions of the patent statutes thisinvention is described. as embodied in concrete form and the principlethereof has been described, together with the modes in which it is nowcontemplated applying that principle, it will be understood that theapparatus shown and described is merely illustrative and that theinvention is not limited thereto, since alterations and modificationswill readily suggest themselves to persons skilled in the art withoutdeparting from the true spirit of this invention or from the scope ofthe annexed claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A tunable strip transmission line resonant circuit comprising a striptransmission line resonant circuit in the form of a strip transmissionline ring, means physically spaced from said resonant circuit to coupleenergy into said resonant circuit to excite said resonant circuit intoresonance, means to vary over a wide range the resonant frequency ofsaid strip transmission line resonant circuit by acting upon theelectric field thereof at the low frequency position and upon themagnetic field thereof at the high frequency position, said widefrequency range varying means consisting of a solid metallic elementinserted within the inner periphery of said ring in a concentric fashiontherewith, and rotatable about the axis thereof, and means physicallyspaced from said resonant circuit to couple out the energy from saidresonant strip transmission line circuit.

2. A tunable strip transmission line resonant circuit comprising a striptransmission line resonant element in the form of a strip transmissionline ring and having a mean circumference of one wavelength, meansphysically spaced from said resonant element to couple energy into saidresonant element, means to vary the resonant frequency of said ring overa wide range by acting upon the electric field thereof at the lowfrequency position and upon the magnetic field thereof at the highfrequency position, said wide frequency range varying means consistingof a metallic element inserted within the inner periphery of said ringand rotatable about the axis of said ring, and means physically spacedfrom said resonant element to couple out the energy from said striptransmission line resonant element.

3. A tunable strip transmission line resonant circuit comprising a striptransmission line resonant element in the form of a strip transmissionline ring with a mean circumference of one wavelength, means physicallyspaced from said resonant element to couple energy into said striptransmission line resonant element to excite resonance therein, means tovary over a wide range the resonant frequency of said ring, said widefrequency range varying means consisting of a solid metallic elementpositioned within the inner periphery of said ring and being in the formof a butterfly concentric to said ring and rotatable about the axis ofsaid ring, and means physically spaced from said resonant element tocouple out the energy from said strip transmission line resonantelement.

4. A tunable strip transmission line resonant circuit comprising a striptransmission line element in the form of a strip transmission line ring,means physically spaced from said ring to couple energy into said ringfor excitation of resonance therein, means to vary the resonantfrequency of said ring over a wide range, said wide frequency rangevarying means consisting of a metallic element grooved at the outerperiphery thereof and being concentric with and rotatable about the axisof said ring, said ring being disposed within said groove, and meansphysically spaced from said ring to couple out the energy therefrom.

References Cited by the Examiner UNITED STATES PATENTS 2,409,449 10/1946Sanders et a1. 333--84 2,892,163 6/1959 Todd 333-73 2,922,123 1/1960Cohn 33384 HERMAN KARL SAALBACH, Primary Examiner.

ELI SAX, Examiner.

1. A. A TUNABLE STRIP TRANSMISSION LINE RESONANT CIRCUIT COMPRISING ASTRIP TRANSMISSION LINE RESONANT CIRCUIT IN THE FORM OF A STRIPTRANSMISSION LINE RING, MEANS PHYSICALLY SPACED FROM SAID RESONANTCIRCUIT TO COUPLE ENERGY INTO SAID RESONANT CIRCUIT TO EXCITE SAIDRESONANT CIRCUIT INTO RESONANCE, MEANS TO VARY OVER A WIDE RANGE THERESONANT FREQUENCY OF SAID STRIP TRANSMISSION LINE RESONANT CIRCUIT BYACTING UPON THE ELECTRIC FIELD THEREOF AT THE LOW FREQUENCY POSITION ANDUPON THE MAGNETIC FIELD THEREOF AT THE HIGH FREQUENCY POSITION, SAIDWIDE FRE-